1. Field of the Invention
The present invention relates to a continuous cleaning system, and more particularly to a continuous cleaning system using a liquified compressed gaseous solvent mixture.
2. Description of the Related Art
Conventional solvent-aided cleaning processes for cleaning sensitive substrates such as fabrics or delicate electronic components have generally used dry cleaning solvents such as perchloroethylene. Due to concerns of air pollution, potential ozone depletion, occupational health and safety, and waste disposal, conventional dry cleaning solvents are being replaced with other less hazardous cleaning fluids. For these reasons, the eventual replacement of petroleum based solvents and chlorinated hydrocarbons as solvents would be desirable.
The use of a liquified compressed gaseous solvent or solvent mixture is being investigated as an alternative to conventional dry cleaning solvents. Some liquified gases are good solvents and remain in liquid phase at near ambient temperature if kept pressurized. These properties make liquified compressed gases desirable for use as solvents in cleaning processes. In particular, liquid carbon dioxide in a supercritical state has been used in garment cleaning processes to remove contaminants from garments.
One such dry cleaning system using supercritical carbon dioxide for dry cleaning of fabrics is disclosed in U.S. Pat. No. 5,267,455. In that system the cleaning is accomplished by agitation of the clothing within a pressurized vessel containing carbon dioxide in a supercritical state. The carbon dioxide is then drained, vaporized and then condensed to remove the contaminants which have been removed from the fabric. The carbon dioxide may then be reused in the cleaning system. However, it would be desirable to be able to continuously clean articles without the need for interruptions in the process to load and unload articles, and to depressurize and repressurize a cleaning chamber.
U.S. Pat. No. 5,313,965 discloses a continuous operation supercritical fluid treatment process in which items are processed in a continuously pressurized main process vessel by use of an entry airlock and an exit airlock. However, due to the high pressures necessary to achieve a supercritical state of the solvent in the system of U.S. Pat. No. 5,313,965, expensive high strength vessels are required.